The increasing complexity of electronic devices, and integrated circuits, coupled with the decreasing size of individual circuit elements, place ever more stringent demands on fabrication processes, particularly with respect to resolution and accuracy of the fabrication patterns. The ability to fabricate on a nanometer scale guarantees a continuation in miniaturization of functional devices, in for example, in microelectronic circuitry as well as other applications.
One class of nano-structures are carbon nanotubes (CNT's) which have attracted much attention because of their dimensions and predicted structure-sensitive properties. Carbon nanotubes have a diameter on the order of a few nanometers and lengths of up to several micrometers. These elongated nanotubes consist of carbon hexagons arranged in a concentric manner with both ends of the tube capped by pentagon-containing, buckminsterfullerene-like structures. Nanotubes can behave as semiconductors or metals depending on diameter and chirality of the arrangement of graphitic rings in the walls. Additionally, dissimilar carbon nanotubes may be joined together allowing the formation of molecular wires with interesting electrical, magnetic, nonlinear optical, thermal and mechanical properties.
The unusual properties of nanotubes suggest a diverse number of applications in material science and nanotechnology, including new materials for electron field emitters in panel displays, single-molecular transistors, scanning probe microscope tips, gas and electrochemical energy storage, catalysts, protein/DNA supports, molecular filtration membranes, and energy-absorbing materials (see, for example: M. Dresselhaus, et al., Phys. World, Jan. 33, 1988; P. M. Ajayan, and T. W. Ebessen, Rep. Prog. Phys., 60, 1027, 1997; R. Dagani, C&E News, Jan. 11, 31, 1999).
It is known that the atomic arrangement in a carbon nanotube, and hence its electrical properties, may vary drastically along the length of the nanotube (Collins et al., Science, 278, 100 (Oct. 3, 1997)). Such a variation in electrical properties may adversely affect the efficiency of electron transport between nano-devices interconnected by the carbon nanotube. Hence, for most of the above applications, it is highly desirable to produce a well-defined specific range or ranges of nanotube lengths such that the properties of individual nanotubes can be assessed and be incorporated effectively into devices. However, existing technology does not provide a means for producing nanotubes of either uniform length, or a well-defined range of length distributions, nor does it provide a means for the rapid and controlled cutting of nanotubes to specific dimensions.
JP 07172807 describes an attempt at controlling the length of generated CNT's. CNT's are irradiated with ions of an appropriate mass and energy sufficient to sever C atomic bonds, producing dangling bonds around the entire circumference of the nanotubes. New CNT's are then grown from these dangling bonds. The method is effective for the cutting of a single CNT however suffers from some significant deficiencies such as an empirical ion selection process and an inability to control the size and length of the newly generated CNT's.
Yudasaka et al., (Appl. Phys., 71 (4): 449–451 (2000) attempts to solve this problem through the use of ultrasonic-homogenization with only moderate success. The method is labor intensive requiring intensive ultrasonic-homogenization in the presence of a polymer solution, filtration, and purification steps and is limited to only single-wall carbon nanotubes.
Lithographic processes have been used for the physical modification of materials on the nano scale. Many of these processes are well developed and include photolithography, interference lithography (sometimes called holographic lithography, see E. Anderson, C. Horowitz, H. Smith, Applied Physics Letters, 43, 9, 874, 1983), immersion lithography (see for example M. Switkes, M. Rothschild, J. Vac. Sci. Technol. B 19, 6, p 2353–6, 2001), X-ray lithography, electron-beam lithography and ion-beam lithography, micro-contact printing (μCP), mechanical scaping, micromolding, (see for example, Dai L., J. Macromol. Sci., Rev. Macromol. Chem. Phys. (1999) 39, 273), soft lithography (see for example Y. Xia, G. M. Whitesides, Annu. Rev. Mater. Sci., 28, p. 153–84, 1998), nanoimprint lithography of the thermal type (see for example S. Y. Chou, P. R. Krauss, P. J. Renstrom, Science, 272, p. 85–87 1996), and the photosensitive type such as step and flash imprint lithography (see for example, M. Colburn, A. Grot, M. Amistoso, B. J. Choi, T. Bailey, J. Ekerdt, S. V. Sreenivasan, J. Hollenhorst, C. Grant Willson, Proc. SPIE Vol. 3676 p. 379–389 1999). However, in spite of the highly developed state of lithographic technology, only a few of these techniques have been applied to solving the problem of generating CNT's having uniform physical parameters (Fan et al., Science, 283, 512, (1999), Huang et al., Yoneya et al., Appl. Phys. Lett. 79,1465–1467, (2001), Dai L., Radiation Phys. and Chem. 62, 55–68, (2001)).
The methods described above may be applied to cut CNT's and other nanostructures on a small scale however are not easily adapted for industrial scale CNT modification. Additionally these methods suffer from the limitation of being unable to reproducibly generate populations of nanostructures having uniform physical parameters of length, width, diameter and area. Applicants have solved this problem by providing a method for generating populations of nano-structures and particularly nanotubes having uniform physical properties by cutting large numbers of aligned nanotubes using lithographic technology.